Cathode ray tube



Dec. 10, 1968 ISAMU NIWA CATHODE RAY TUBE Filed se t'. 21, 1964 3 Sheets-Sheet l 4 mm N W 1 m m m I a r//////// r/ l// I u H u x 1 HEW;

ISAMU NIWA Dec. 10, 1968 CATHODE RAY TUBE s Sheets-Sheet 2' Filed Sept. 21, 1964 Prior ar-Z Prior arZ Intel-1.77:1 Isamu M'u/a CATHODE'RAY TUBE 3 S e sat 5 Filed Sept. 21, 1964 he 1 She 1112511773: /sa.mu Nz'wa United States Patent 3,416,026 CATHODE RAY TUBE Isamu Niwa, Tokyo, Japan, assignor to Sony Corporation, Tokyo, Japan, a corporation of Japan Filed Sept. 21, 1964, Ser. No. 397,783 12 Claims. (Cl. 315-31) ABSTRACT OF THE DISCLOSURE In a post-deflecting and focusing cathode ray tube, wherein the grid is supported on a frame, an auxiliary electrode is mounted adjacent to the frame at an edge portion of the grid wires. The auxiliary electrode is provided with a suitable potential and is properly spaced in relation to the grid wires for cancelling a gradient of potential which exists across the grid wires due to the presence of the frame potential which undesirably influences the grid equi-potential lines.

This invention relates generally to cathode ray tubes, and more particularly to a method of post deflecting and focusing an electron beam and to a post deflecting and focusing (PDF) color cathode ray tube such as the chromatron tube.

As is well known in the art, parallel grid wires are utilized in the post deflecting and focusing type of cathode ray tube. A grid frame extends around an inside peripheral portion of the phosphorous screen of the tube and is employed primarily for supporting the grid wires in their respective desired positions. For obvious reasons, the grid frame must be maintained at grid potential. In such a' case, however, both end portions of each grid wire are dilferent from the center portion thereof in its potential distribution. As a result, the lens effect in the edge portions of the grid structure is weaker than that obtained in the central portions. The present invention is intended, therefore, to provide a novel method and means for compensating for the edge effect of the grid on the electron stream.

Accordingly, it is a primary object of the present invention to provide an improved cathode ray tube.

It is another object of the present invention to provide a post deflecting and focusing type color cathode ray tube wherein the potential distribution is substantially equal at all points on the grid structure.

It is still another object of the instant invention to provide an improved cathode ray tube for the reconstruction of polychrome images wherein a so-called colorrunning or fog is eliminated at the peripheral portions of the phosphorous screen and images of high fidelity are accordingly reproduced thereon.

Still another object of the present invention is to provide an improved cathode ray tube which will illuminate the screen thereof with a constant diameter illuminating spot throughout the entire area thereof.

It is another object of the present invention to provide a method of obtaining a uniform diameter for an electron stream impinging on the screen of a cathode ray tube.

Another object of the present invention is to provide an improved cathode ray tube in which a specific electrode is so positioned with respect to the grid wires and the grid frame and is disposed at a suitable potential with respect to the grid potential to provide a high quality picture representation on the screen.

These and other objects of the present invention will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a semi-schematic and cross-sectional view illustrating a preferred embodiment of a post deflecting 3,416,626 Patented Dec. 10, 1968 and focusing cathode ray tube according to the present invention;

FIGURE 2 is a cross-sectional view of the cathode ray tube taken along line IIII of FIGURE 1;

FIGURE 3 is a partial sectional view taken along line III-III of FIGURE 2 with the electrode structure of the present invention removed therefrom to illustrate the prior art;

FIGURE 4 is a partial sectional view taken along line IV-IV of FIGURE 2 and is also shown with the electrode of the present invention removed therefrom to illustrate the prior art;

FIGURE 5 is a broken out detailed view shown in perspective of the grid structure and electrode of the present invention;

FIGURE 6 is a graph illustrating the relationship of a voltage applied to the electrode of the present invention with respect to the grid voltage and the diameter of the electron stream or beam spot; and

FIGURE 7 is a diagrammatic partial sectional view of the present invention illustrating the masking effect produced thereby.

Like reference numerals throughout the various views of the drawings are intended to designate the same or similar structures.

With reference to the drawings in detail, and in particular to FIGURE 1, there is shown one preferred embodiment of the present invention. A cathode ray tube, generally designated with the reference numeral 1, includes an electron gun 3 positioned in a neck portion 2 thereof. Various types of electron guns are well known, but the one illustrated by the present exemplification includes an electron-emitting cathode 4, which in operation is raised to emitting temperature by a heater. A control electrode or grid 5, in the form of a cup, surrounds the cathode. A second grid 6, a third grid 7 and an anode 8 are included within the neck portion 2 of the cathode ray tube 1 for additional electron beam control.

Stripe-like phosphor layers 10 of at least two colors are coated on the inner face of a face panel 9 and comprise the screen pontion of the cathode ray tube 1. The screen also includes a conductive coating generally designated with the reference numeral 12 which may, for example, be an aluminum layer. A grid 11 is disposed in spaced relationship and in relatively close proximity to the screen portion. The grid 11 includes a plurality of vertically extended grid wires 11', to which are applied switching voltages for proper color selection.

A shield electrode 13 is mounted within the cathode ray tube for reducing the velocity of an electron beam 14 emitted from the electron gun 3. Furthermore, the electron beam is protected from an external disturbance field and/or a free secondary electron. A deflection coil 15 is mounted at the junction of the neck portion 2 and a funnel portion 16 of the cathode ray tube 1 for providing proper deflection of the electron beam 14 toward the screen portion.

As is well know, the ratio of a voltage V applied to the grid 11 and a voltage V applied to the phosphor screen 10 is substantially 1 to 4. As a result, the electron beam 14 is re-focused by a static electron lens. Such refocusing is accomplished by the electric field existing between the grid structure and the screen portion. This static electric field is represented by equal potential lines 17, 18 and 19 shown in FIGURE 3. In such a case, the electron beam 14 is focused or converged to produce a beam spot having a diameter D which is usually on the order of 0.1 millimeter. However, the equal potential lines illustrated in FIGURE 3 are representative only of the potential distribution at the central portion between the grid and screen.

As illustrated in FIGURES 1 and 2, the grid wires 11' are supported on a grid frame 20 which extends around the peripheral portion of the screen of the cathode ray tube 1. The grid frame 20 is maintained at the static grid potential V Therefore, the electric field at the peripheral portions between the grid and the screen is substantially altered as illustrated in FIGURE 4. This effect is especially pronounced at the upper and lower edge sides of the screen, for example, in that area as illustrated in FIGURE 4. In such a case, equal potential lines designated with the reference numerals 21, 22 and 23 respectively are illustrative of the electric field due to the potential of the grid fra 1e 20. In this area of the screen, the diameter of the beam spot D becomes relatively larger and is on the order of between 0.2 to 0.3 millimeter. Therefore, the lens effect at the edge portions of the cathode ray tube is weaker and less pronounced than that at the central portions.

As is more clearly illustrated in FIGURES 3 and 4, the phosphor layer 10 includes a plurality of phosphor stripes for producing red, green and blue color images each respectively designated R, G and B. Each of these color stripes are activated when deflection of the electron beam 14 is accomplished by a switching voltage V applied to the grid wires 11'. Opposite polarities of the switching voltage V with respect to the grid potential V are applied to alternate grid wires to effect the deflection of the electron beam 14 to the respective color stripes.

In view of the fact that the static potentials produce a gradient of potential and electric field, the diameter of the beam spot on the phosphor stripes will vary between the edge portions and the central portion of the screen. Accordingly, by the present invention, compensation of the gradient of potential is realized to effect a substantially uniform and sufficiently small diameter of the beam spot at all portions of the screen. In the preferred exemplification of the present invention illustrated herein. platelilte or annular electrodes 26 are positioned at the edge portion of the grid, particularly in the vicinity of ends 24 and 25 of each grid wire 11 as is particularly illustrated in FIGURE 1. Electrode 26 is supported in relative proximity to the grid 11 and includes one flange portion thereof extending toward a center axis -0 of the cathod ray tube 1. The grid wires 11 are secured by means of a cement 27 to the frame 20 and the electrode 26 and shield 13 are secured to the frame 20 through an insulating material 28.

The exemplified grid structure and the relationship of the electrode 26 thereto is better illustrated in FIGURE 5, since particular minute details could not be illustrated in the other views of the drawings with facility. The grid wires 11 are insulated from the grid frame 20 by an insulator 28a and from one another by an insulator 28b. As shown, the alternate grid wires are supplied with opposite polarities with respect to the grid voltage V of the switching voltage V The grid frame 20 is maintained at the grid potential V and the electrode 26 is maintained at a potential V.

The graph of FIGURE 6 represents the relationship between the diameter D of the beam spot and the potential V of the electrode 26 less the grid potential V The family of curves designated with the reference numerals 29, 30 and 31 each define a constant parameter of the distance d between the grid 11 and the electrode 26. In the exemplified illustration, the curves 29, 30 and 31 define distances of 4, 11 and 20 millimeters respectively. As is apparent from the graph, the diameter D decreases with an increase in the potential V of the electrode 26 on the curves 30 and 31. As shown by the curve 31, for example, a potential in excess of 1,000 volts is required to obtain a diameter D of about 0.1 millimeter for the electron beam spot on the screen structure.

However, such operating conditions are impractical and when the distance d is decreased as illustrated by the curve 29 in FIGURE 6, an optimum point designated with the reference numeral 32 will be obtained wherein the electron beam diameter is relatively small for a potential ditference of approximately 600 volts. Although, as apparent from the curve 30, the electrode 26 may be spaced at a distance of 11 millimeters, it is preferably spaced at a distance of less than 5 millimeters from the grid 11 so that a potential difference between the electrode 26 and the grid frame 20 of less than 1,000 volts may be employed. According to the present experimental results with the exemplified structure illustrated, when the electrode 26 was spaced at a distance d of four millimeters from the grid 11, electron beam diameters of 01 millimeters were obtained on the screen structure as shown by the curve 29.

With the structure of the present invention including the electrode 26, the edge effect previously mentioned is eliminated and the lens action across the entire grid structure is essentially the same. Therefore, in the present invention, sharp images of good focus can be obtained.

Furhtermore, additional advantages have been realized by the structure of the present invention. That is, when one edge of the electrode 26 projects toward the center axis of the cathode ray tube 1, it provides a masking effect with respect to the electron beam 14. Such advantage is better illustrated in FIGURE 7 wherein, if the electrode 26 were removed, an electron beam, illustrated by the dotted line 14', would directly impinge the grid frame 20. Such direct impingement of the electron beam on the grid frame 20 would cause secondary electron emission from the frame structure. In the present invention, however, the beam directed to the frame 20 is masked by the electrode 26, thereby preventing the occurrence of secondary emission. In view of the foregoing, it is preferable that the electrode 26 disposed at the peripheral portion of the frame 20 be annular in shape.

The principles of the invention explained in connection with the specific exemplifications thereon will suggest many other applications and modifications of the same. It is accordingly desired that, in construing the breadth of the appended claims they shall not be limited to the specific details shown and described in connection with the exemplifications thereof.

What is claimed is:

1. A cathode ray tube comprising (a) a screen including a plurality of phosphor stripes for emitting respective light color components in response to electron impingement therewith,

(b) a grid mounted adjacent said screen including a frame and wires fixed to said frame in substantially parallel relationship with respect to said phosphor stripes,

(c) an electron gun, and

(d) an electrode disposed substantially perpendicular to said grid and being spaced substantially equally from each of said wires, said electrode being mounted on said frame and projecting toward a center axis of the tube.

2. The cathode ray tube of claim 1 wherein said electrode is spaced a distance of less than 11 millimeters from said grid.

3. The cathode ray tube of claim 1 wherein said electrode is supplied with a voltage of up to 1,000 volts with respect to a voltage applied to said grid.

4. In a cathode ray tube having a screen, an electron gun disposed for emitting an electron stream toward the screen, grid wires disposed in relative proximity to the screen, and a frame supporting the grid wires and disposed for producing a gradient of potential thereon, the improvement therein comprising electrode means disposed in substantial equal proximity to the ends of said grid wires for cancelling the effect of the gradient of potential on the electron stream.

5. The cathode ray tube of claim 4 wherein said electrode means includes an annular plate extending around the entire edge portion of the grid.

6. The cathode ray tube of claim 4 wherein said electrode means is spaced from the edge portion of the grid a distance of less than 11 millimeters.

7. The cathode ray tube of claim 4 wherein said electrode means is disposed at a potential of 600 volts with respect to a potential on the grid.

8. The cathode ray tube of claim 7 wherein said electrode means is spaced from the edge portion of the grid a distance of 4 millimeters.

9. The cathode ray tube of claim 7 wherein said elec trode means extends along the entire length of the frame.

10. The cathode ray tube of claim 9 wherein said electrode means extends from the frame toward a center axis of the cathode ray tube.

11. A cathode ray tube comprising (a) a screen,

(b) an electron gun,

(c) a grid structure including a frame extending about a peripheral portion of said screen and spaced a suitable distance therefrom, said grid structure including a plurality of grid wires supported on said frame,

((1) means for insulating said grid wires from said grid frame and alternate ones of said grid wires from one another,

(e) a signal source disposed at a suitable potential and having opposite signal polarities with respect to said suitable potential connected to respective alternate ones of said grid Wires, and

(f) electrode means extending along the entire length of said frame and having a portion thereof spaced s-ubstantially equally from the ends of said grid wires and insulated therefrom for cancelling an electric field from said frame and realized on an electron stream emitted from said electron gun and passing through said grid wires.

12. A cathode ray tube comprising (a) a screen,

(b) a screen including a plurality of phosphor stripes for emitting respective light color components in response to electron impingement therewith,

(c) an electron gun,

(d) means for deflecting an electron stream from said electron gun disposed in relative proximity to said screen and at a suitable grid potential, and

(e) means disposed adjacent to the ends of said wires for focusing the electron stream at an edge portion of said grid, said means being disposed at a distance of substantially 4 millimeters from said grid and at a potential of substantially 600 volts with respect to the grid potential.

References Cited UNITED STATES PATENTS 2,914,691 11/1959 Evans 313-78 RODNEY D. BENNETT, Primary Examiner. B. L. RIBANDO, Assistant Examiner.

US. Cl. X.R. 313-78 

